Gas separation is useful in many industries and can typically be accomplished by flowing a mixture of gases over an adsorbent material that preferentially adsorbs one or more gas components while not adsorbing one or more other gas components. The non-adsorbed components are recovered as a separate product.
One particular type of gas separation technology is swing adsorption, such as temperature swing adsorption (TSA), pressure swing adsorption (PSA), partial pressure swing adsorption (PPSA), rapid cycle temperature swing adsorption (RCTSA), rapid cycle pressure swing adsorption (RCPSA), rapid cycle partial pressure swing adsorption (RCPPSA), and not limited to but also combinations of the fore mentioned processes, such as pressure and temperature swing adsorption. As an example, PSA processes rely on the phenomenon of gases being more readily adsorbed within the pore structure or free volume of an adsorbent material when the gas is under pressure. That is, the higher the gas pressure, the greater the amount of readily-adsorbed gas adsorbed. When the pressure is reduced, the adsorbed component is released, or desorbed from the adsorbent material.
The swing adsorption processes (e.g., PSA and/or TSA) may be used to separate gases of a gas mixture because different gases tend to fill the micropore of the adsorbent material to different extents. For example, if a gas mixture, such as natural gas, is passed under pressure through a vessel containing an adsorbent material that is more selective towards carbon dioxide than it is for methane, at least a portion of the carbon dioxide is selectively adsorbed by the adsorbent material, and the gas exiting the vessel is enriched in methane. When the adsorbent material reaches the end of its capacity to adsorb carbon dioxide, it is regenerated by reducing the pressure, thereby releasing the adsorbed carbon dioxide. Then, the adsorbent material is typically purged and repressurized prior to starting another adsorption cycle.
The swing adsorption processes typically involve adsorbent bed units, which include adsorbent beds disposed within a housing and configured to maintain fluids at various pressures for different steps in a cycle within the unit. These adsorbent bed units utilize different packing material in the bed structures. For example, the adsorbent bed units utilize checker brick, pebble beds or other available packing. As an enhancement, some adsorbent bed units may utilize engineered packing within the bed structure. The engineered packing may include a material provided in a specific configuration, such as a honeycomb, ceramic forms or the like.
Further, various adsorbent bed units may be coupled together with conduits and valves to manage the flow of fluids through the cycle. Orchestrating these adsorbent bed units involves coordinating the steps in the cycle for each of the adsorbent bed units with other adsorbent bed units in the system. A complete cycle can vary from seconds to minutes as it transfers a plurality of gaseous streams through one or more of the adsorbent bed units.
Conventional processes are used to treat hydrocarbon containing streams containing CO2 and H2O to prepare the stream for nitrogen rejection specifications. For example, a gas stream containing higher amounts of CO2 is treated using solvents (e.g., amines, selexol and the like) or cryogenic processing (e.g., controlled freeze zones (CFZ), Ryan Holmes and the like) to a CO2 specification closer to the nitrogen rejection process specifications. Subsequently, the stream is cleaned using a final polishing step using a conventional molecular sieve, which removes the CO2 to the nitrogen rejection specification and dehydrates to nitrogen rejection specifications. Such stringent specifications are not applied on gas streams in typical Natural Gas Liquid (NGL) recovery systems. As such, for nitrogen rejection systems, additional treatment steps may be necessary for a feed stream.
Unfortunately, conventional processes for processing feed streams for a nitrogen rejection system have certain limitations. With nitrogen rejection operations, the size and weight of the conventional system, which are molecular sieve units, may be problematic. The operational costs of the gas treating process decreases as the product gas specification become less stringent. However, increases in the load on the molecular sieves results in the molecular sieve units becoming large and expensive. As such, there is a need to increase the range of the final polishing step to reduce the load on the initial gas treating step and improve the overall process costs. These problems are further compounded for floating facilities. The excessive weight and footprint for conventional systems add to the complexity of the floating facility and increase the size of the facilities. Also, the additional size and complexity increase the capital investment costs along with the operating costs for the floating facilities.
Accordingly, there remains a need in the industry for apparatus, methods, and systems that provided enhancements to the processing of feed streams into a nitrogen rejection system. Further, a need exists for a reduction in cost, size, and weight of facilities for treatment of feed streams prior to nitrogen rejection unit.